The invention relates to a method for masking noise as well as a control device and a masking system for carrying out said method.
It is known from the reference EP 0 376 482 A2 to employ noise masking systems in open-plan offices and similar premises to ensure confidential conversations in a confined space. The need for the possibility to exchange information in a zone of a room despite the presence of other persons exists in banks, for example.
It is further known from the reference EP 0 376 482 A2, in the respective premises, to generate a permanent background noise in the entire room or confined to limited zones of the room for noise masking purposes in order to camouflage voices and prevent more remote persons from following conversations.
However, human beings try to instinctively drown out a sound source. A permanently present sound source thus results in persons speaking louder than actually necessary. In FIG. 4 this correlation becomes apparent. This is also known as “Lombard effect”, such as from “H. V. Fuchs, Schallabsorber and Schalldämpfer, Springer-Verlag Berlin Heidelberg, 2007”. Background noises having high sound levels may cause hearing problems which in turn cause persons to speak up. This results in a higher auditory threshold which in turn causes persons to speak up. In this cause-effect spiral the sound pressure levels are getting louder and louder until they become unbearable in the end. Typical masking systems give additional support to this effect. Such a masking sound source has thus to be adjusted at a volume higher than necessary if a human being spoke with usual sound intensity. Nevertheless, it cannot be achieved that confidentiality is observed in this way, since human beings will always speak up with increasing volume of the masking noise.
Another system for masking noise is known from the reference EP 1 291 845 A2. A loudspeaker is used to generate noise with such frequencies that are able to specifically camouflage human speech. An air diffuser which houses the loudspeaker helps to direct the sound into the room in which human voices are to be masked. Said device can be equipped with a microphone which is used to identify the appearance of external noise and only after the appearance and registration of external noise does the loudspeaker of the masking system generate sound due to masking purposes.
This noise masking system is also disadvantageous in that human beings will automatically speak up with the generation of the masking noise. A relatively loud masking noise has thus to be generated in order to achieve the desired masking effect.
It is known from the German patent application 102007000568 to absorb in rooms above all noises having a frequency within a range of about 200 and about 700 Hz in offices and the like by a respective sound absorber in order to ensure a quiet atmosphere in offices. A quiet atmosphere is supposed to guarantee good work performances. If it is very quiet in an office, however, human beings are especially sensitive to occurring noises and are easily distracted by quietly appearing noises in particular. Above all related noises occurring in a quiet atmosphere reduce the work performance. FIG. 5 illustrates this correlation by means of a study on the effect of train noises on the cognitive performance of school children in second class. The comprehensibility upon playing in two different train noises into a class room was practically not changed compared to the reference measurement without any static noises. In contrast, playing in foreign language caused a significant decrease in comprehensibility of more than 20%. Although this static noise did not contain any useful information for the second graders, as none of them was able to understand the foreign language, the work performance was reduced merely due to the related way of speaking.
If, in accordance with the theory known from the reference EP 1 291 845 A2, a relatively low masking noise was generated in such cases only upon the appearance of external noise, this would notably interfere with the ability to concentrate and thus the work performance of persons present in such a room.